The invention relates to improvements in thermoplastic polyesters and especially to polyester compositions including poly(C.sub.2 -C.sub.4 alkylene terephthalate) such as polybutylene terephthalate (PBT).
PBT or other poly(C.sub.2 -C.sub.4 alkylene terephthalates) have been widely used in molding compositions including molding compositions which also contain impact modifiers and aromatic polycarbonates. U.S. Pat. Nos. 3,864,428, 4,257,937, 4,180,494 and 4,280,948 for instance teach the use of such polyester resins in molding compositions which also include aromatic polycarbonate of the type described in U.S. Pat. No. 4,034,016 together with core-shell type impact modifiers. Polyester molding compositions including PBT, aromatic polycarbonate and aromatic polyester carbonate are also known and are described for instance in U.S. Pat. No. 4,226,961. While these various prior art formulations are satisfactory for many purposes they have mechanical and thermal properties which are not completely satisfactory for some applications.